Geometry and deformation features of the most recent co-seismic surface ruptures along the Xiaojiang Fault and its tectonic implications for the Tibetan Plateau

摘要

The Anninghe, Zemuhe, Xiaojiang and Daliangshan faults bound the southeastern margin of the Tibetan Plateau, which has almost been entirely ruptured by strong earthquakes during the past 500 years. The geometry and deformation features of the most recent co-seismic surface ruptures show not only the surface morphology of the source seismogenic fault, but also the structural characteristics of the upper crust, as well as the pre-existing tectonic environment. Hence, the most recent co-seismic surface ruptures along the Xiaojiang Fault zone reveal the surface deformation of the southeastern Tibetan Plateau. Our investigation reveal that the 1833 Songming rupture zone is about 150 km, with maximum co-seismic offset of 8.4 m, and the re-evaluated moment magnitude is about M 7.5-7.6 which is lower than previously estimated M 8.0. The 1500 Yiliang rupture zone is about 80 km, with maximum co-seismic offset of 8.0 m, and the re-evaluated moment magnitude of M 7.2-7.5, which is higher than previously demonstrated M 7.0. The spatial distribution of the surface rupture zones along Xiaojiang Fault shows an arcuate geometry. Our findings also reveal that strong earthquakes rupture not only the two major strands but also the en echelon faults between them. The arcuate geometry of the fault zone and the development of these en echelon faults are consistent with the clockwise rotation of the southeastern Tibetan Plateau.